Simultaneous electron-photon excitation of hydrogen and helium

Abstract

Total and differential cross sections for simultaneous excitation of H(2s), H(3s) and He(1s 2s) by electron impact in the presence of a photon field have been calculated in second-order perturbation theory. The characteristics of the results are interpreted in terms of their physical origin. The off-shell excitation cross section for the He(1s 2s) state is found to be one order of magnitude smaller than that for excitation of the H(2s) state. This is consistent with our expection that atoms with higher dipole-polarisability should favour larger off-shell cross sections for transitions betweens-states.

The authors like to thank Prof. H. Kleinpoppen (University of Stirling) for many helpful discussions.